The present invention relates to a toroidal continuously variable transmission.
In a toroidal continuously variable transmission (hereafter, CVT), an input disk and output disk arranged face to face grip a pair of power rollers. The power rollers gripped therebetween transfer a torque from the input disk to the output disk by friction. The power rollers are supported rotatably by trunnions.
If the trunnions displace in the trunnion axis direction in mutually opposite directions, the power rollers gyrate with the trunnions, and as a result, the contact circle radius with one of the input disk and output disk increases, while the other contact circle radius decreases. The variation of these contact circle radii causes a variation of the rotation speed ratio of the input disk and output disk, i.e., a speed ratio. Thus, the speed ratio of the transmission can be varied continuously by displacing the trunnion in the trunnion axis direction. The rotation angle about the trunnion axis as pivot is referred to as the power roller gyration angle, and directly corresponds to the speed ratio of the CVT.
Here, the pair of power rollers are gripped between the input disk and output disk by a thrust force generated by a loading mechanism. Due to the force, the pair of power rollers tend to displace in a direction separating them, and the pair of trunnions which support the power rollers also tend to displace in a direction separating the trunnions. To prevent this displacement, the upper ends and lower ends of the trunnions are connected by an upper link and lower link, respectively. During speed change, the trunnions displace in mutually opposite directions along the trunnion axis, and also gyrate around the trunnion axis as pivot. The trunnions are joined to these links via combination joints which combine a bearing and a spherical joint.
In general, the links are supported in the transmission so that they are only rotatable around pins as pivots, as disclosed by JP-A-H9-317837 published by the Japanese Patent Office in 1997.
During speed change, the trunnions displace in mutually opposite directions in the trunnion axis direction as above-mentioned. However, in the structure wherein the links are supported via the pins, if the trunnions and links interfere, the pins function as a pivot so that a force in the same direction acts on the trunnions.
For example, if one trunnion pushes a link from the bottom, this trunnion receives a downward force from the link, and a downward force will also act on the other trunnion with the pin as a pivot. Consequently, the synchronism of the trunnions is disturbed and they do not displace in mutually opposite directions correctly.
If they do not displace in synchronism, the forces acting on the power rollers from the disks are not equal, and if one of the forces becomes large, the power roller on which the large force acts may slip between the disks.
To suppress this slip, the force with which the disks grip the power rollers must be increased, but to increase the grip force, a loading cam which generates a large thrust force is required, and the strength of various parts must be increased to withstand this grip force. This tends to increase the size of the transmission.
It is therefore an object of this invention to prevent links from exerting forces in the same direction on ions even if the trunnions and links interfere with each other.
It is a further object of this invention to prevent links from interfering with components other than trunnions.
In order to achieve the above objects the present invention provides a toroidal continuously variable transmission, comprising an input disk, an output disk facing the input disk, power rollers gripped between the input disk and output disk, trunnions which support the power rollers rotatably, and a link jointed to the trunnions, which limits the displacement of the trunnions in the power roller rotation axis direction, and is supported free to displace in the trunnion axis direction in a transmission case.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.